Rig tuning and set up
Westaway Sails’s guide to Rig setup
This is a very general guide to setting a Hunter Impala 28 rig. Westaway Sails can provide a championship winning sails complete with a detailed tuning guide to alter the rigging to suit various conditions.
The object of this guide is to offer an initial starting point, which will offer competitive mast set up for various different sail manufacturers.
|Conditions||True Wind Strength||Rigging Tension
New Loos Gauge
Caps / Lowers
Old Loos Gauge
Caps / Lowers
½ turns from Base
|Survival||Above 25 knots||39 / 32||42 / 35||Caps + 13, Lowers||No.3 or 4|
|Heavy||18 – 25 knots||38 / 31.5||41 / 36||Caps = 10, Lowers + 13||No.1 or 2|
|Medium (Base)||10 – 28 knots||33 / 17||36 / 25||Base||No.1|
|Light||5 – 10 knots||25 / 10||31 / 15||Caps – 6, Lowers – 3||No.1|
|Drift||Less than 5 knots||20 / slack||24 / slack||Caps – 9, Lowers – 6||No.1|
First things first
First you will need to ensure that the mast is completely upright (sideways) in the boat. You will need to tension all four shrouds hand tight. Attach a long steel tape measure to the main halyard and hoist to the top of the mast. Measure down to the aft quarters of the deck (the top of the deck port and starboard as far aft and outboard as possible). Tension the cap shroud on the side of the yacht that gave the largest reading. It is wise to only adjust 2 turns on the rigging screw at a time, then tension the lower shroud to keep the spar in column sideways. Re-measure and repeat the exercise until the mast is upright and in column sideways.
Most Impalas use 6mm 1×19 or 6mm dyform shrouds. Smaller 5mm shrouds are allowed in the class rules but stretch in stronger winds. For the purpose of rig tensions we have assumed that your Impala has 6mm dyform shrouds. You can purchase a rig tension gauge which will enable you to repeat shroud tensions. The most common gauge is a ‘Loos’ gauge. The original ‘Loos’ gauge is named Model B, this model gives similar but not identical readings to a meter supplied by the spar makers ISP better known as Superspars. In the last year or so a more accurate meter called the ‘Loos professional tension gauge’ (Model PT-2M) has been put onto the market and this is the model we recommend.
As a starting point we suggest that you tension the shrouds so that both the cap and lower shrouds read 37 on the ‘Loos’ gauge. This is very much a guide starting point which shroud be competitive in around 15 knots of wind.
As a guide cap shroud tension affects the tension in the forestay and as a result it affects the yachts pointing ability. A tight forestay allows a flat entry to the genoa and therefore high pointing and less power. A sagging forestay reduces pointing but increases power. In stronger winds (15 knots and above) pointing upwind is very important as the yacht has already reached near maximum boatspeed. In very strong winds you may feel the need to increase the cap shroud tension to around 40. In lighter winds pointing the boat upwind is not as important as boatspeed so we recommend easing the capshroud tension to around 25.
Lower shroud tension affects primarily the fore and aft bend in the mast. If with the mainsheet on, and the backstay eased, the mainsail has creases running from the clew to the luff up to about half way up the mast, then the mast is too bent and you should increase the lower shroud tension. Keep increasing this tension until the creases only reappear when the backstay is pulled on to maximum. If the mainsail is excessively full even when the backstay is on hard then the lower shrouds are too tight and should be eased. The tensions for the lower shrouds will vary for mainsail to mainsail. In light airs it is quite possible to need the mast totally straight (fore and aft) with the lower shrouds very slack to avoid the mainsail being too full. For medium wind strengths we suggest a mast bend with no backstay of 1 inch and for stronger winds maybe more depending on the shape of the mainsail.
Adjusting the rigging
When adjusting the rigging on the water either lower sails to adjust, or only adjust the leeward shrouds when sailing upwind then tack to adjust the other side. Attempting to adjust with shrouds under load may result in stripping the threads on the rigging screws and risks mast failure.
In general the mast rake (ie the angle off the vertical) can affect the upwind and downwind feel and performance of the yacht. Raked well aft the mast will improve upwind performance, hinder downwind performance and increase weather helm. A more upright mast will reduce weather helm or may even incur lee helm, improve downwind but hinder upwind performance. Never have a mast with a completely upright or forward raked mast.
With 1 inch of prebend for and aft in the mast, with no mainsheet, vang, halyards tension or backstay, you should have a measurement of 12.225m from the top of the mast to the very aft quarters of the deck (top of the deck port and starboard as far aft as possible) and 11.40m from the top of the mast to the deck adjacent to the base of the shrouds.
To measure this you will need a calm day and a long steel tape measure. Do not forget to add the length of the snap shackle and knot or splice on the main halyard, so the distance measured is from the reference point to the main halyard sheave.
Westaway Sails have won the IRC National championships in 2000 and the Impala European championships in 1999 and 2000.
A more detailed rigging tensions guide for varying conditions to be used in conjunction with Westaway Sails is available upon ordering new sails. Contact Sean Semmens or Simon Unwin on 01752 892560.
This came from the Impala forum:”We recenty bought some sails from Steve Goacher up in Windermere and I spoke to him re setting up the rig. He told me to set the mast with 18″ of rake, (use the main halliard to ensure that the mast is central in the boat by measuring each side to the chainplate) tighten the outers as much as you can (dare) by hand (no big levers). take the slackness out of the inners then take the boat out ideally in 12 – 15 knots of constant breeze (how you organise this i’m not sure).
Start beating then, looking at the outers first, if they are slack, tighten by a maximum of two turns, we did one at a time, then go onto the opposite tack and do the same. Tack back again, check the outers, if they are still slack repeat the process, if they are just moving slightly they are about right. at this point look at the main to see if there are any creases running from the spreaders to the end of the boom, if there is you will need to tighten the inners do this in the same way as the outers 1 -2 turns at a time tack over and repeat, tack back and check until you are satisfies that the main has a nice shape & no creases. If the creases are running the length of the mast you may need to reduce tension in the main halliard or reduce the tension of the inners to obtain the desired shape in the main. check the jib and position of the care to make sure that the telltales are all breaking correctly.
This worked for us as our boat drives really well upwind and is well balanced with no weather helm and is well balanced downwind also.